Conventionally, a liquid rotor-type tachometer and an eddy-current tachometer have been known as an angular acceleration detector for detecting an angular acceleration of a rotary body.
The liquid rotor-type tachometer, as shown in FIG. 15 in which the structure thereof is illustrated, detects movements of a liquid instead of those of the pendulum of a servo-type acceleration detector, and measures a value of a feedback electrical current applied to a servo system in order that the servo system realizes a balanced condition with respect to the movement of the liquid, to thereby determine an angular acceleration according to the measured feedback electrical current. More specifically, the liquid 2 is enclosed in a ring-shaped tube 1 and is partitioned by a paddle 3. When the tachometer itself begins to rotate, the liquid tends to stay at an absolute position and therefore the paddle dividing the liquid is angularly deflected by a force applied thereto. A deflection detector 4 detects this deflection and supplies a torquer with a feedback electrical current in order to return the paddle 3 toward a zero position. Since the value of the feedback electrical current is proportional to an amount of angular acceleration occurred, the occurred angular acceleration can be determined in accordance with the instant feedback electrical current.
On the other hand, as shown in FIG. 16, the eddy-current tachometer is constituted in that a permanent magnet is used to form a magnetic circuit and a cylindrical aluminum rotor is disposed in the circuit so that an angular acceleration is detected based on a magnetic electromotive force occurred in accordance with a change in rotational speed of the rotor.
However, since the liquid rotor-type tachometer is limited in a range of measuring rotational angle, it has a defect that it cannot detect a angular acceleration over an infinite rotational range. While, the eddy-current tachometer needs to be provided with a high-sensitive signal processing circuit because detected signals are extremely weak.
An object of the present invention is, in consideration of the above defects, to provide an angular acceleration detector capable of detecting a angular acceleration of a rotary body over an infinite rotational angle.